Geographic Range

Snowy owls have a circumpolar distribution. They breed in coastal Alaska, Canada, and Greenland, as well as in northern Scandinavia, Russia, southern Novaya Zemlya and northern Siberia. In winter, snowy owls can be found in Canada and the northern United States, sporadically further south into the U.S., in Iceland, the British Isles, northern Europe, central Russia, northern China and Sakhalin. While typically found in the arctic, periodic irruptions of "excess populations" occasionally move south, driven by a lack of food resources in the tundra. Snowy owl fossils have been found as far south as the Tropic of Cancer, and are believed to have originated in that region. (Encyclopedia Britannica, 1995; Hoyo, et al., 1999; National Geographic, 1999; Parmelee, 1992)

Habitat

Snowy owls inhabit open tundra, usually from sea level to less than 300 m elevation. They may also inhabit lowland salt grass meadows and poorly drained freshwater wet meadows, especially for hunting. When food is scarce, snowy owls travel south to warmer climates in winter. Prime winter habitat in the Great Plains is similar to their breeding habitat. In the south, they are frequently seen in villages and urban centers, as well as in marshes and on dunes. (Parmelee, 1992)

Physical Description

Snowy owls are the largest bird species in the arctic, 63 to 73 cm long with an average wingspan of 170 cm. Females are larger and heavier than the males, weighing 1550 to 1600 grams, compared to males which weigh 1450 to 1500 grams. Snowy owls are predominantly white with dusky brown spots and bars. Females tend to have more markings than males, which may become nearly completely white as they age. Young snowy owls are generally darker and more heavily marked than adults. Snowy owls have yellow eyes and their legs and feet are covered in white feathers that protect them from the cold weather. (Grzimek, 1972; Kielder Water Bird of Prey Centre, 1999; Living Planet, 1999; Parmelee, 1992)

Reproduction

Snowy owls are generally monogamous, though polygyny has been reported in a few instances when prey was excessively abundant. Breeding pairs may form on the wintering ground or after the owls reach the breeding ground in late April or early May. There is no evidence that pair bonds last beyond one breeding season.

Elaborate courtship displays are associated with breeding pair formation and early breeding activities. The male performs an “aerial display” followed by a “ground display’. The “aerial display” consists of an exaggerated undulating flight, frequently while carrying a lemming in the bill or claws, followed by a gradual climb and finally a gentle vertical descent to the ground. Once on the ground, the male performs the “ground display”. With his back toward the female, the male stands erect and then leans forward with his head lowered and tail partly fanned until he is nearly lying on the ground. Another infrequently observed display is the passing of a lemming from male to female while in flight. (Parmelee, 1992)

Snowy owls usually breed between May and September. Individuals arrive on the breeding grounds beginning in late April, though breeding pairs may form earlier on the wintering grounds. The male of a pair establishes a territory, and the female selects a nest site, which is a low windswept prominence, such as a hillock, hummock or boulder. The female constructs a nest by scraping out a shallow bowl in the turf or bare ground. The nest is not lined with any insulating materials. The female then begins laying eggs at 2-day intervals. Clutch size is usually 3 to 11 white eggs, depending on prey availability, but can be as large as 16 when prey are extremely abundant. The female incubates the eggs, beginning with the first egg laid. The chicks hatch asynchronously after 32 to 34 days (average 31.6 days) of incubation. The eggs hatch approximately every other day leading to a wide range in size and age of chicks within a nest. The female broods the chicks until they abandon the nest. Both parents feed and protect the chicks, which are covered with snowy white down. The male brings food to the nest, where the female dissects it into smaller pieces to feed to the chicks. Chicks begin to leave the nest before they can fly, 14 to 26 days after hatching. The parents continue to feed them for 5 to 7 weeks until they are able to hunt for themselves.

The age of sexual maturity is not known for this species, though it is likely to me at least two years old. Adult snowy owls are able to breed annually if prey abundance allows. In years of low prey abundance, snowy owls forgo breeding. Snowy owls generally raise only one brood per breeding season. However, if a nest fails early in the breeding season, snowy owls may re-nest. (Parmelee, 1992)

Snowy owl females lay and incubate the eggs for an average of 31.6 days. After hatching, the female broods the semialtricial chicks until they leave the nest at age 14 to 25 days. Both parents defend the nest by dive-bombing potential predators that approach the nest and using distraction displays to draw the predator away from the nest. The male brings food to the nest for the chicks. The female processes the food by tearing it into smaller pieces before feeding it to the chicks. After the chicks leave the nest, both parents continue to feed and protect the chicks for 5 to 7 weeks. (Parmelee, 1992)

Behavior

Snowy owls are generally solitary and territorial. Males establish territories on the breeding grounds and defend them using vocalizations and threat postures. Territory size varies with prey abundance; during years of abundant prey, as many as five pairs may hold territories within a square mile whereas pairs are much more widely spaced during years of scarcity. During the winter, females establish territories, which they defend until spring, when they fly north.

Snowy owls are migratory. However, migration in this species is unpredictable and likely related more to prey abundance than seasons or weather. In general, snowy owls move nomadically, and breed when and where prey is abundant. Approximately every four years, many snowy owls irrupt into the northern United States during the winter, presumably because prey is scarce further north.

Home Range

There is no information available regarding the home range of snowy owls. (Parmelee, 1992)

Communication and Perception

Snowy owls utilize sight, sound and touch to communicate and perceive their environment. Males “hoot” more frequently than females, and seem to use this vocalization in territorial defense and establishment. Males and females also give a variety of other calls, including a “rick, rick, rick”, a “kre kre kre”, a mewing and a hiss. These vocalizations are frequently used when the adult is disturbed near the nest.

Physical displays are frequently used to communicate. For example, males use courtship displays to attract a mate (See Mating Systems), and exaggerated posturing when threatened or when defending a territory from a neighboring male. (Parmelee, 1992)

Food Habits

Snowy Owls are carnivorous. They hunt by utilizing an elevated perch that affords them good visibility while waiting for potential prey to appear in the hunting area. Visual scanning of the hunting area is facilitated by their ability to swivel their head three quarters of the way around (270 degrees). Snowy Owls' main foods are typically lemmings and mice. However, they also take rabbits (family Leporidae), seabirds, and fish opportunistically. If extra food is captured, snowy owls may store it on a nearby perch. (Chinery, 1992; Parmelee, 1992)

Predation

Humans are probably the most important predator of snowy owls. Snowy owls are killed by humans for food, trophies, and to protect game animals. Other predators include foxes, jaegers, and probably dogs, wolves and other avian predators.

Males defend the nest by standing guard nearby while the female incubates the eggs and broods the young. Both sexes attack approaching predators, dive-bombing them and engage in distraction displays to draw the predator away from the nest. (Parmelee, 1992)

Economic Importance for Humans: Positive

Snowy owls play a part in controlling populations of lemmings and other rodents. However, given their arctic distribution, this has little economic effect on humans. (Grzimek, 1972)

Positive Impacts

controls pest population

Economic Importance for Humans: Negative

Snowy owls have been known to raid traplines set out by trappers. Over time they have learned to follow these traplines regularly, costing trappers game animals. (Grzimek, 1972; Hoyo, et al., 1999)

Conservation Status

The global population of snowy owls is estimated at about 290,000 individuals, and appears to be stable. This species is classified as a species of “least concern” by the IUCN red list, and is not considered endangered or threatened in the United States. It is protected under the U.S. Migratory Bird Act and CITES Appendix II. The most common causes of mortality of snowy owls include collisions with vehicles, utility lines and airplanes, gunshot wounds, electrocution and entanglement in fishing tackle. (BirdLife International, 2004; Parmelee, 1992)

Contributors

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal

active during the day, 2. lasting for one day.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

Found in northern North America and northern Europe or Asia.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.